Roughly 42 million people around the world are infected with HIV (AIDS). In 2003 alone, there were five million cases of HIV infection and three million people died from AIDS. One fourth of the patients were unaware they had the virus and could unknowingly pass the virus onto others. Currently, there is no cure for AIDS.
A number of laboratory methods are available to screen blood, diagnose infection, and monitor disease progression in individuals infected by HIV. These tests can be classified into those that (a) detect antibodies, (b) identify antigens, (c) detect or monitor viral nucleic acids, and (d) provide estimates of T-lymphocyte numbers (cell phenotyping).
Of these methods, antibody detection is the most widely used and most effective in identifying HIV infection. Such tests include Enzyme-Linked Immuno-Sorbent Assays (ELISA), Western Blots, and Indirect Fluorescent Antibody (IFA) tests.
ELISA stands for “enzyme-linked immunosorbent assay”. This screening test is usually the first test that is used to detect infection with HIV. One common feature to all varieties of ELISA is the use of enzyme conjugates that bind to specific HIV antibodies, and substrates/chromogens that produce color in a reaction catalyzed by the bound enzyme conjugate.
A Western blot test, which is harder to perform and interpret than an ELISA test, is usually done to confirm the results of two positive ELISA tests. A typical Western blotting technique consists of the following parts: (1) separation of polypeptides by SDS-PAGE; (2) electro-transfer of separated proteins from the gel onto the blotting paper; (3) labeling of the transferred proteins by antibodies conjugated with the enzyme; and (4) detection of the labeling enzyme signal.
Indirect Fluorescent Antibody (IFA) tests can be used to detect antibodies that are made to fight an HIV infection. Like a Western blot test, it is used to confirm the results of ELISA tests. IFA tests are more expensive than Western blot tests.
While the above-described antibody tests are effective, HIV antibodies generally do not reach detectable levels until 1-3 months following infection. For example, it sometimes takes up to 6 months for antibodies to be generated in large enough quantities to show up in standard blood tests.
Another type of test is P24 antigen testing. P24 antigen is a protein that is part of the HIV virus. Early in the infection process, P24 antigen is produced in excess (each particle of the virus contains about 3,000 molecules of the p24 protein) and can be detected in the blood serum by a commercially available test. The P24 test can detect HIV infection before the body develops enough detectable viral antibodies.
Yet another type of test is a Plasma Viral Load (PVL) test. There are several different plasma viral load tests. Two are currently approved for general use. The first one is called the Amplicor HIV-1 Monitor test, better known as the PCR test. The other is called NucliSens HIV-1 QT or NASBA. These tests were approved by the FDA to check the health of people with HIV. The Plasma Viral Load test measures the quantity of RNA of the HIV virus in human plasma.
For people who are already diagnosed with AIDS, a T-lymphocyte (also called CD4+, a type of white blood cell) count measurement can be performed regularly to monitor how the HIV virus affects the immune system. (It is well known that HIV infects CD4+ cells.) Most people infected with HIV who are not being treated experience a gradual drop in the number of CD4+ cells over time. The number of CD4+ cells indicates the health of the immune system and the likelihood that opportunistic infections may occur.
The above tests are useful, but are fairly time- and sample-consuming. For instance, ELISA results are usually available in two to four days. Results of other tests, such as the Western blot or IFA, take as long as one to two weeks.
It would be desirable to provide for a improved tests and testing methods. Embodiments of the invention address these and other problems.